1. Field of the Invention
The present invention relates to a seat back of a vehicle seat, and in particular relates to a seat back structure in the seat wherein a separate mat member is fitted in the recessed area formed in the frontal surface of seat back.
2. Description of Prior Art
Among hitherto seat back structures in vehicle seats, there has been a seat having such seat back structure wherein a separate mat member is fitted in the recessed area of the seat back by means of a hook-like male latch member and a wire female latch member, which are latched together for securing the separate mat member onto the recessed area of the seat back. This sort of seat back structure is known from the U.S. Pat. application No. 706,223 to the assignee, an owner of the present invention. For a brief explanation of that prior art, reference is made to FIGS. 1 and 2, which show a seat back structure including a seat back body (SB) formed by a covering member (11) and cushion member (12), an integral head rest (HR), an air ventilation opening (H) defined between the seat back body (SB) and headrest (HR), a recessed area (12b) formed in the frontal surface of the seat back body (SB), and a separate mat member (M). Within the seat back body (SB), there is embedded a seat back frame (13), and further within the upper part of the cushion member (12), there is embedded a plate frame member (14) extending between both lateral frame sections of the seat back frame (13). The plate frame member (14) is formed with a pair of spaced-apart male latch members (15)(15) of a hook-like shape. Each of the male latch members (15)(15) is formed by punching out the corresponding part of the plate frame member (14) in the outward direction, with a reinforcing bead (15b) formed centrally of the latch member (15) and with a stopper lug (15a) formed at both lateral edges of the same latch member (15). Designation (14a) denotes an opening which is left after forming the latch member (15). As shown, a pair of spaced-apart cut-away areas (12c) (12c) are formed at the foregoing upper part of cushion member (12), whereupon the two male latch members (15) (15) are respectively projected in the respective two cut-away areas (12c) (12c). Designations (11) (11) denote a pair of lateral bolster portions of the seat back (SB). The mat member (M) comprises a cushion member (20), a frame (24) embedded therein, a covering member (21) affixed over the cushion member (20), and a securing wire (24). The securing wire (24) is formed such that its both ends are embedded in the cushion member (20) and welded to the respective lateral frame sections of frame (24), and its center portion is bent into a pair of spaced-apart U-shaped female latch members (23) (23), which are exposed upon the rear surface of cushion member (20). The two female latch members (23) (23) are disposed at the upper part of cushion member (20) corresponding to the two male latch members (15) (15) of seat back body (SB).
Thus, according to this prior art, the mat member (M) is secured in the recessed area (12b) of seat cushion body (SB) by engaging the female latch members (23) (23) over the male latch members (15) (15), respectively, and connecting the lower extension cloth (25) of mat member (M) with that (16) of seat back body (SB), using a suitable securing member such as hog rings.
Referring now to FIG. 2, the female latch member (23) has a width (W1) slightly smaller than that (W2) of male latch member (15). When the former (23) is engaged over the latter (15), in normal cases, the horizontal portion of the former is engaged with the two stopper lugs (15a) of the latter. Thus, the female latch member (23) is prevented by the stopper lugs (15a) against removal from the male latch member (15). However, it is found that an external load applied from the back of an occupant sitting on the seat to the mat member (M) or repeated vibrations given thereto will bring the female latch member (23) out of the stopper lugs (15a) into contact with both lateral edges 14b of opening (14a) of plate frame (14), emitting an unpleasant noise therefrom.